Circuit interrupter



Apl 4, 195o H l- RAWLINS HAL 2,502,992

CIRCUIT INTERRUPTER Filed Dec. 16, 1943 @WER/W Patented 4, 1950 2.50amclacm'r INTEBBUPTEB Herbert L. Rawlins, Pittsburgh, and Harold 1I.

Fahnoe. Wilkinsburg, inghousc Electric Corporation,

Pa., alsignors to West- East Pittsburgh,

Pa., a corporation of Pennsylvania Application December 16, 1943, SerialNo. 514,502 25 Claims. -(Cl. F75-294) This invention relates, ingeneral, to electric circuit interrupting devices and, moreparticularly, to high voltage fuses which are especially adapted tolimit the current and voltage at least upon interruption of heavyoverloads and short circuits.

The copending application oi' H. H. Fahnoe on Circuit interrupters,Serial No. 511,562, flied November 24, 1943, now issued at Patent No.2,483,577, dated October 4, 1949, and assigned to the same assignee ofthis invention represents a recent development in current'and voltagelimiting fuses, of the teachings of the copending application of H. L.Rawlins, Serial No. 357,393, filed September 19, 1940 now Patent No.2,337,495, issued December 21, 1943, and the intermediate developmentsas represented in the copending application of A. P. Strom, Serial No.357,395, filed September 19, 1940 now Patent No. 2,337,504, issuedDecember 21, 1943, and H. L. Rawlins, et al. Patent No. 2,309,013,issued January 19, 1943, all assigned to the same assignee of thisinvention. This prior work teaches that an eilicient current and voltagelimiting fuse should comprise, in general, three main elements asfollows: (l) a current limiting fusible element capable of producing ahigh arc voltage in a fraction of a half cycle, preferably in a fewhundred microseconds after the fusible element melts, to limit thecurrent at a low point in its rise, and to effect a transfer of thecurrent to, (2) a resistor which is connected in parallel with thefusible element to limit the voltage and current to a predeterminedvalue; and (3) a clean-up fusible element to interrupt the power followcurrent through the resistor.

While this general arrangement may be used throughout for fuses of allcurrent ratings, this invention is primarily concerned with the solutionof certain special problems encountered in fuses of this type for thehigher current ratings, for example, in current ratings of about tenamperes and above. While a fuse of this typecould be constructed inaccordance with the prior disclosures mentioned above for such highlcurrent ratings, by merely enlarging these prior structures, theresulting fuse for ratings, for example, of one or two hundred amperes,would be excessively large in size and too costly. To build a fuse ofthis type in the higher current ratings by merely increasing the size ofthe current limiting fusible element, as by merely providing a pluralityof parallel fuse wires, would necessitate a much larger structure forthe absorption of metal vapors on melting the fusible 2 element, andwould require an excessively large parallel resistor to handle thehigher currents.

It is, accordingly, one object of this invention to provide a currentand voltage limiting fuse of the general type described, of a novelconstruction especially adapted for high current ratings, but which issmall in size and economical of manufacture.

Another object of this invention is to provide a novel fusible elementhaving a time characteristic especially adapted to fuses of this type.

Another object of this invention is to provide a novel structure forsupporting a current limiting fusible element to obtain a high arcvoltage in an extremely short time upon fusion of the element, with aminimum of disturbance.

Another object of this invention is to provide a novel unitary assemblyof current limiting fusible means and shunt resistance means.

Still another object 'of this invention is to provide a. novel powerfuse assembly which is responsive to light continuing overloads as wellas heavy overloads to eiilciently interrupt the circuit.

These and other objects of this invention relating to certain noveldetails of fuse construction and assembly, .will become more apparentupon consideration of the following description of a preferredembodiment of the invention, when taken in connection with the attacheddrawing, in which:

Figure l is a substantially central longitudinal section through a fuseconstructed in accordance with this invention, with certain of the partstherein shown in elevation;

Fig. 2 is an enlarged partial transverse crosssection view of thelimiter unit employed in the fuse shown in Fig. l, taken substantiallyon the line II-H thereof;

Fig. 3 is an enlarged partial longitudinal section taken through one ofthe slots of the fuse supporting member shown in elevation in Fig. l;and

Fig. 4 is a curve illustrating the melting characteristics of thefusible element employed in the structures shown in Figs. 1 to 3.

The particular embodiment of the invention disclosed is illustrated asbeing mounted within a tubular fuse holder 2 of insulating material,such as ilber or a synthetic resin. The tubular fuse holder 2 isprovided with terminal caps l and 6 adapted to be secured over theopposite ends of the tubular holder. Terminal caps 4 and 6 may be oi'any desiredconducting material, such, for example, as copper or thelike, and they are preferably secured in position on tubular holder 2but having indentations 8 rolled therein, and staking pins I may be alsoprovided to prevent relative rotation of the terminal caps and tubularholder.

The actual current and voltage limiting means disclosed are embodied ina limiter unit I2 adapted to be secured in position within one end oftubular holder 2. The limiter unit I2 includes a supporting tube I4 ofsuitable insulating material such as ber or the like, provided with endterminal caps I6 and I8 threadedly engaged over each end of supportingtube I4. Terminal caps I6 and I8 of the limiter unit may be of any goodelectrical conducting material such as copper, brass, or the like. Theparticular current and voltage limiting means constituting thisinvention are adapted to be supported by supporting tube Id, withcertain of the elements mounted within the tube, and others supported onthe outside of the tube between terminal caps i6 and i8.

In order to effectively provide for current and voltage limitation onhigh overloads and shortcircuits, it is necessary that the overload belimited before the maximum current is obtained in the first half cycleof the overload. If this is not done, the resulting surge on the firsthalf cycle of fault current is capable of doing considerable damage'tothe circuit and especially to connected apparatus, such as transformersand the like. Accordingly, the main problem encountered in obtainingeffective limiting action is to render whatever current limiting meansemployed, eiective soon enough that it can operate to prevent the riseof the fault current to its maximum value in the first half cycle. Thismeans that the current limiting means must be rendered effective in asmall fraction of a half cycle of such overloads as it is desired tolimit, on the order of time of a few hundred microseconds. This problembecomes acute in fuses having a continuous current rating above ten.amperes, because considerable time is needed to melt the relativelylarge fusible elements required, and it is difficult to obtain a highenough arc voltage after fusion of the fusible element with suiiicientspeed to exert a limiting action on the current in a device of practicalsize. This invention comprehends one particular structure which iscapable of limiting the current and voltage in the rst half cycle of thefault, in a device which is small in size, and, therefore, capable ofpractical application.

The particular means for obtaining current and voltage limitation inlimiter unit I2, comprises a supporting rod 20, which extendslongitudinally Within supporting tube I4 and is preferably of aninsulating material which is capable of evolvingan arc extinguishing gaswhen in proximity with an electric arc, such, for example, as iiber or asynthetic resin. It will be noted that supporting rod 20 is considerablysmaller than the internal diameter of supporting tube I4 and iscentrally positioned therein so as to be spaced from the inner Walls ofthe supporting tube. Supporting rod 20 is provided with substantiallycentral bores at each end, for a purpose to be described. A plurality oflongitudinally extending slots 22 are provided in supporting rod 20,angularly spaced around the periphery of the rod. These slots 22 are forthe purpose of receiving fuse wires 24, which are connected at theirends to terminal disks 26 and 28. Terminal disks 26 and 28 have integralcentrally located positioning pins 21 and 29, respectively, adapted tobe 4 received in the bores at the ends of rod 20. These terminal disksare of a good electrical conducting material, such for example, ascopper or the like, and are slotted to correspond with the slots 22in-supporting rod 20 for receiving the fuse wires 2'4 which are securedin the slots of the disks, for example, as by soldering or the like.Terminal disk 26 is provided with an integral threaded stud 3D for apurpose to be described, and the other terminal disk 28 is provided withan integral terminal extension 32 having a diametrically extending slotin the outer end thereof, which will be hereinafter referred to. Aplurality of washers 3e are telescoped over supporting rod 2U and aredisposed in spaced relation along the length of the supporting rod, fora purpose to be described. Washers 3i may be .of any desired insulatingmaterial, such, for example, as ber or the like.

As stated above, the most important factor in obtaining eflicientcurrent limitation is the speed at which the current limiting operationis brought into play, at least on overloads which it is desired tolimit. Since the first thing that must occur on such heavy overloads isthe fusion of the fusible element to establish an arc, it is absolutelynecessary that the fusible element in a fuse of this type be capable offast action, especially on those heavy overloads where it is desired toexert a current limiting action. In the above-mentioned patent of H. H.Fahnoe, No. 2,483,577, the limiter fuse wires are disclosed as being amaterial such as silver which has a high electrical conductivity and lowspecific heat to obtain fast melting time on high overcurrents. Anotheradvantage of this material is that it has a relatively high temperaturecoeicient'of resistance so that the resistance will increase at arelatively rapid rate just prior to melting. Although ordinary fusewires of uniform diameter, made of silver or other materials havingcomparable'characteristics, are suitable for use in a current limitingfuse having a low current rating, for example, ten amperes or less,fuses of higher current ratings, which must be designed with a greateramount of fusible material to carry such higher currents, require thatthe individual fusible elements operate considerably faster than theordinary fuse Wire in order that the total melting time be fast enoughto effectively limit the current. Referring to Fig. 3, it will be seenthat the particular fusible elements employed in the fuse of thisinvention are especially constructed to provide a faster action at leaston the higher currents. To this end, the fuse wire itself is chosen tobe of substantially the same size as that required to carry the ratedcurrent without undue heating, and which will melt on currents above therated current. Such a wire is then provided with a plurality of reducedarea sections 36, such, for example, as by rolling these sections. Ithas been found that by making the fuse wire with sections 36 reduced inarea, the fusion time of the wire is speeded up to correspond to that ofa wire of substantially the same diameter as the reduced sections forhigh values of current. This speeding up effect has been found to beroughly proportional to the ratio between the areas of the largeportions of fuse wire 24 and reduced portions 36. As a practical matter,this ratio may be made as high as possible, being limited only bymechanical strength consideration. Such a fuse wire retains all thenormal time-current characteristics desired in a fuse for time values inexcess of approximately two cycles without appreciable reduction incurrent carrying ability. Reduction one-fourth cycle, fuse wire 24 hasan exceptionally fast melting time. This will be clear from aconsideration of Fig. 4 of the drawing wherein the characteristictime-current curve of a fuse wire constructed in accordance with thisinvention is shown in full lines. The particular fuse element having thecharacteristic curve shown in Fig. 4 has a diameter of .036 inch andreduced portions 34 of .0145 inch. Fig. 4 illustrates the time currentcurve extended in dotted lines for a fuse wire of uniform diameter andlike material having a diameter of .033 inch, and the other dotted linecurve illustrates the time current characteristic for a fuse wire of auniform diameter of .016 inch. It will be observed that by providing thereduced sections 36, the fuse wire still retains substantially the sametime-current characteristic on low currents up to about 400 amperes as afuse wire of a uniform diameter substantially equal to the largediameter of the fuse wire constituting this invention. However, oncurrents above 400 amperes, fuse wire 24 is much faster, yand departsabruptly from the characteristic of the large diameter wire and becomessubstantially coincident with the characteristic of a fuse wire having auniform diameter substantially the same as the reduced section 26 ofi'use wire 24. This means that a fuse wire constructed with reducedsections 36 will have its continuous current carrying abilitysubstantially unimpaired, and even its time current characteristic onlight overloads will be substantially unchanged. However, on heavyoverloads, and this is particularly important and useful with currentlimiting fuses where it is desired to limit such heavy overloads; onsuch overloads, the fuse wire constructed in accordance with thisinvention operates much faster, and, accordingly, it is possible tobring the current limiting means into action soon enough, so that it maybe effective at an early point in the rst half cycle of fault current.While the particular fuse wire disclosed has a special cooperation in a.current limiting fuse in order to permit early limitation of thecurrent, it may, of course, ilnd application in connection with otherfuse structures of general utility.

Actual current limitation is effected in this fuse by providing a higharc voltage upon fusion of fuse wires 24, which arc voltage is built upsubstantially instantaneously to thereby exert a limiting or chokingeiect on the overload current and prevent its rise beyond apredetermined value. In order that the length of the fuse may be keptdown to a reasonable amount, it is necessary that the arc volts per inchof length of the arc be made a high value, not only to obtain a highvalue of arc voltage but to cause this high value of arc voltage to beattained with the greatest possible speed. One way of increasing the arcvoltage per inch of arc length, is to provide a relatively large numberof reduced sections 36 in fuse wire 24, so that when these reducedsections melt, a plurality of serially related arcs will be struck, andthe summation of the arc voltages of these series arcs will then begreater than the arc voltage across a single arc. Generally speaking,the arc voltage per inch is directly proportional to the number ofseries or restrictions Il per inch. This Butgests that to obtain maximumarc voltage, there shouldube provided as many restrictions per inch asphysically possible. However. this is not literally true, because as thenumber of restrictions 36 per inch areincreased a point is eventuallyreached where a further increase results in a decrease inl currentcarrying ability. This appears to be due to the resulting reduction inlength ofthe large diameter fuse wire portion to the point where they nolonger have sufllcient mass to absorb enough of the heat generated inthe restrictions 26 to maintain the temperature of the restrictionsbelow the fusion point. It has been found that at least for voltagesabove 600 volts atleast two restrictions 20 per inch of fuse wire 24, ora total of l0vshould be provided to obtain an eilective rise in arcvoltage in a fuse wire which is not of excessive length. 'Ihiscorresponds approximately to a spacing of restrictions 36 not to exceedabout l5 times the large diameter of the fuse wire. It is desirable,however, to use the maximum number of restrictions possible withoutsubstantially impairing the current carrying ability of the fuse wire.Such a desirable number of restrictions will depend on the size of fusewire employed, In the particular example previously given, with a wirehaving a diameter of .036 inch, the restrictions 36 should be spacedabout oneeighth of an inch apart, for best results. This particularspacing of reduced sections 36 corresponds roughly to 3.5 times thelargest diameter of the fuse wire. This is an optimum spacing, howeverspacings as low as, about twice the largest diameter of the fuse wiremay be employed with good results. The specific example given above isfor a fuse wire designed for a fuse to have a continuous current ratingof 200 amperes at 2500 volts. Such a fuse will employ eight fuse wires24 connected in parallel between the terminal caps I6 and i8 of limiterunit I2.

Another aid in rapidly building the arc voltage up to a high enoughvalue to exert a current limiting e'ect, is the narrow slots 22 in whichfuse wires 24 are located. The width of slots 22 is made as small aspossible, being limited only by the size of fuse wires 24, and inpractice the slots may be made not more than .010 inch larger than thefuse wires. This clearance will provide a snug i'lt of the wires in thebase of the slots, and since the slots are preferably made about twiceas deep as the diameter of the fuse wires, itis apparent that the wireswill closely contact the slot on three sides, that is, at the bottom andopposite sides of the slot. The use of such narrow slots in which thearc is struck upon melting of the fusible elements, physically restrictsthe lateral boundaries of the are, thereby raising the arc voltage atthe instant the arc is formed.

Because fuse wires 24 are in intimate engagement with the walls of slots22 in the supporting rod, and since the rod is of a material capable ofevolving an arc extinguishing gas, it will be apparent that the arcformed upon fusion of reduced sections 36 will be in close proximity onthree sides with the walls of the slots so that considerable quantitiesof arc extinguishing gas will be evolved, and this gas will blastlaterally through the arc to perform three functions, all of which actto increase the arc voltage. First, the blast of arc extinguishing gasthrough the arc acts to sweep metal vapor out of the arcy stream tothereby increase the resistance and,l

consequently, the voltage across the arc. This metal vapor is swept outof the slots by the arc extinguishing gas and into the material`38filling the space between supporting rod and supporting tube I4.Material 38 is preferably an inert granular insulating material, such,for example, as sand or the like, and this acts to disperse and condensethe metal vapors into separated particles insulated from each other bythe particles of sand, so that a high resistance path is maintainedoutside the slots. Secondly, the blast of arc extinguishing gastransversely of the arcs in the slots, also .acts to supply unionizedgas to the arc path, which obviously increases the resistance of the arcpath and, consequently, the voltage drop across it. A third function ofthe transverse gas blast is to cause the series arcs to be loopedoutwardly towardthe lling material 38, thereby lengthening the arc pathand, consequently, increasing the resistance thereof and the voltagedrop across it. The function of washers 34 on supporting rod 20 will nowbe apparent, as permitting looping of the series arcs outwardly of slots22, but preventing these arcs from entirely escaping from the slot and,consequently, from proximity with the gas evolving material, and fromthe restricting action of the narrow slot, while preventing the arcsfrom restriking as a single arc outside of the slots. It is apparentthat washers 34 provide spaced points along the slots where the arcscannot escape from the slots, so that any looping of the arcs outwardlyof the slots must occur between washers 34. Washers 34 function the sameway on extremely high currents when the fuse wires may be entirelyconsumed and the arc in each narrow slot may become a single long arc.

From the foregoing, it is apparent that efcient current limitation ofthe rst half cycle of the fault current may be obtained with thestructure disclosed because: (l) the fusible element itself is capableof melting to establish an arc at least on the high currents which it isdesired to limit, in a very short time, that is, in a very smallfraction of a half cycle; (2) as soon as the arc is established, it issubjected to all of the factors enumerated above which create an arcvoltage at the instant an arc is formed which is high enough to preventany further rise of fault current. It has been found that the factorsenumerated, produce such a high arc voltage in an extremely short periodof time, so that the current is actually limited in a small fraction ofthe first half cycle of fault current, on the order of time of a fewhundred microseconds.

While the current is limited essentially by the high arc voltageinstantaneously produced by the fuse Structure contained Withinsupporting tube I4, this arc voltage must at the same time be preventedfrom creating a surge on the circuit which might cause ashover damage toother apparatus connected in the circuit and to line insulation.Accordingly, this voltage is prevented from rising to a dangerously highValue by the provision of a resistance in parallel with the fusestructure within supporting tube I4. This resistance is preferably inthe nature of a resistance wire 48 wound on the outside of thesupporting tube and connected to terminal caps I6 and I8. For thispurpose, each of the terminal caps is provided with an integralsemicircular extension, such as the extension on that the end turn ofresistance wire 48 may abut the cap flanges at one side and lie ingroove 44 or 4o at the other side. is provided with a very thin coatingof insulating material, such, for example, as a glass composition, andis preferably of a material which is substantially non-magnetic and hasa positive temperature coeicient of resistance, such, for example, as acopper-nickel alloy. Actually the resistance wire 48 comprises but asingle wire which is wound, for example, with one end placed in groove46 of terminal cap I6, in an inner layer along tubular holder I4 untilterminal cap I8 is reached, whereupon one half turn is laid in slot 44and an outer layer is then wound over the first layer of winding, andthis will obviously be wound in a direction opposite to the firstwinding, to thereby cancel the inductance of the two windings. The outerwinding is then continued until terminal cap I6 is again reached, andthe end of wire 48 may also be laid in groove 4E, groove 46 isillustrated in Fig. l with one end of wire 48 therein. The resistancewire 48 may be secured in grooves 44 and 4 as by soldering or the like,or by peening over the outer end wall of the slots.

Such a resistance being connected in parallel with the fuse elementswithin tubular support I4, and being non-inductively wound, willstabilize the voltage that occurs during interruption. The maximumvoltage that can appear across the fuse is simply the IR drop throughthe resistor, because as soon as the voltage reaches this value thecurrent will transfer to the resistance circuit. Since the arc voltagein slots 22 builds up at an extremely rapid rate, as previously pointedout, transfer of the current to the resistance will occur in a smallfraction of a half cycle. Thus, knowing the instantaneous peak currentpermitted by the current limiting structure within tubular holder I4,which can be determined from curves made from experimental data, thevalue of resistance 48 may be chosen to limit the voltage to any desiredfigure. In addition to controlling the voltage surge duringinterruption, the resistance very materially reduces the duty on thecurrent limiting fuse elements, because the total energy which isrequired to be absorbed by the current limiting fuse elements has beenfound to be less than 15% of the energy that it would absorb without anyparallel resistance. This also contributes to making possible a verycompact structure, and is a very material factor in the small overallsize of the complete fuse.

The limiter unit I2 may be secured in position within tubular holder 2,by the stud 30 at the upper end thereof, which extends through anaperture provided in terminal cap 4 of the fuse holder 2, and isprovided with a nut 5I) for securing the limiter unit I2 in operativeposition with its terminal cap I8 in conductive relation with terminalcap 4 of the fuse holder 2. Terminal cap I6 of limiter unit I2 isprovided with an integral extension 52 of reduced size, which isexternally threaded for cooperation with internal threads provided inone end of a tube 54 of insulating material, such, for example, as

Resistance wire 48 ber or the like. A cap 50 is provided for the otherend of tube 54, and a spacer tube 51 is adapted to fit in the spacebetween tube 54 and fuse tube 2. Tube 54 has supported therein, betweenextension 52 and cap 58, a lining comprising blocks 58 of a materialwhich is capable of evolving an arc extinguishing gas when 'in proximitywith an electric arc, such, for example, as'boric acid, synthetic resin,or the like. These blocks 58 of gas evolving material have a centralbore therethrough for receiving a strip of fusible material 60,adaptedto be connected to terminal l2 of the limiter unit I2. The stripof fusible material 60 is adapted to flt into the slot provided in theouter end of terminal 32, and to be secured therein by a low meltingpoint solder 62. The strip of fusible material 6U is adapted to have aportion reduced in area, as by the provision of apertures 64 therein todefine a melting point for excess currents. The current carryingcapacity of fusible strip 80.*at least at the section at apertures 64,is somewhat less than fuse wires 24 so that the fusible strip 50 willalways operate first, at least on lower values of overload current. Acoil tension spring 56 has one end hooked through an aperture in theouter end of fusible strip 60, and has the other end anchored to anindicator disk 68 held in a depression at the outside of holder terminalcap 6, by spring 86. 'I'he indicator disk G8 is biased outwardly by arelatively weak coil compression spring 10, reacting between the diskand terminal cap 8. A bushing 'i2 of a good electrical conductingmaterial, such as copper or brass, is provided for the aperture throughwhich the outer end of spring 66 extends, and this bushing is providedwith a nut 14 at the outside of the cap by which it is held in position.Fusible strip 60 is electrically connected with holder terminal cap 6 byflexible shunts 16 of copper or the like, which may be brazed orotherwise secured to the fusible strip and to bushing 12. The space atthe end of tubular holder 2 occupied by tension spring 66 is preferablylined with a metallic fabric or Iscreening 18, to provide means forcondensing gases emitted from gas evolving material 58.

In the operation of the fusible element described above, it will beobserved that it is electrically connected in series between holderterminal caps 4 and 6, with the parallel arrangement of limiter fusibleelements 24 and resistance wire 48. The series fuse may operate upon theoccurrence of relatively light overloads which continue for relativelylong preiods of time by melting of solder 62, due to heat conductingthereto from the fusible element 60. On higher overloads and shortcircuits, the fusible element 60 will melt at the point ldefined byapertures 64, and in either case the outer end of the fusible elementwill be withdrawn by -tension spring 66 through the passage formed bygas evolving material 58, to thus lengthen the arc and subject it to theaction of arc extinguishing gas evolved from material 58. Preferablythis gas evolving material is one which evolves a readily condensablegas, such as water vapor, so that upon expulsion of this gas into thelower end of the fuse tube, it will contact the relatively cool surfacesdefined by metallic material 18, and be condensed to Athereby avoid thebuilding up of high pressures within the fuse holder.

'Ihe operation of the complete device may now be summarized, and it willbe apparent that the fuse may operate in either of two ways, dependingupon the magnitude of fault current. On relatively light overloads, theseries fuse will operate by melting of solder 82 and the resulting arcwill be lengthened and extinguished by the deionizing action of gasesevolved from material 5l, while the metallic material 18 condenses theevolved gas. During this process, the current limiting fusible elements24 do not fuse because of their higher current carrying capacity, andconsequently play nopart in the interruption.

On heavy overloads or short circuits where it is desired to limit thecurrent, the series fuse will operate in a small fraction of a halfcycle. and the current limiting fuse elements will melt substantiallysimultaneously at a, very rapidrate, as previously described. The fusionof the current limiting fuse elements 24 and the action of the resultantseries arcs in the restricted ber slots all act to rapidly produce anarc voltage high enough in value to prevent further increase in thefault current. This occurs in a small fraction of a halt cycle, andtransfer of the current to the resistance 48 is effected at the sametime. The condensing action of the granular insulating material 38within the current limiting unit I2 has the effect of reducing pressureswhich would otherwise be present Within the current limiting unit, notonly by the condensation of metal vapors from the fuse wires themselves,but also by the cooling action thereof on the gases evolved from theinner walls of slots 22. On such operation of the current limiting unit,the current is effectively limited, and the resistance wire 48 preventsa rise in the voltage beyond a predetermined value. The series fuse willarc through the current limiting action, which, as pointed outpreviously, requires only a very short time on the order of a fewhundred microseconds, and the seriesy fuse then interrupts the currentthrough the resistance at the first current zero. Since this current islimited by the resistance, it has a high power factor, and,consequently, itis very easily interrupted.

From the foregoing, it will be apparent that this invention not onlyprovides a current limiting fuse which is capable of efficientlylimiting the value of current in the first half cycle for fuses havinghigh current ratings, but that there is also disclosed herein a novelconstruction of fuse wires to obtain unusually fast action thereof, atleast on high values of current. This invention also comprehends a novelcombination of means for obtaining a high arc voltage in a very shorttime, to thereby obtain its particularly efcient current limitingoperation. These particular novel features are combined with a parallelresistance to limit the voltage and also prevent any further rise incurrent, with this parallel arrangement all supported in a novel mannerin a relatively small and compact arrangement in a tubular holder ofpractical size having an additional fuse element connected in seriestherewith to interrupt the circuit on light overloads, and to finallyinterrupt the current as limited by the current limiting structure onheavy overloads. The whole construction disclosed is totally enclosed sothat no external display or venting of arc products occurs.

Having described preferred embodiments of the invention in accordancewith the patent statutes, it is desired that this invention be notlimited to this particular embodiment inasmuch as it will be obvious,particularly to persons skilled in the art, that many modifications andchanges may be made in these particular structures without departingfrom the broad spirit and scope of this invention. Accordingly, it isdesired that the invention be interpreted as broadly as possible, andthat it be limited only as required by the prior art.

We claim as our invention: l. In a circuit interrupter, a supporting rodof insulating material, a plurality of spaced generally longitudinallyextending slots in the outer surface of said rod, means for striking anarc in each of said slots, and a plurality of washer-like members ofinsulating material mounted in spaced relation on said rod to preventescape of corresponding portions of said arcs from said slots.

2. In a circuit interrupter, a supporting rod of insulating material, aplurality of spaced generally longitudinally extending slots in theouter surface of said rod, a fuse wire in each of at least a pluralityof said slots adapted to automaticallir fuse and establish an arc ineach such slot in response to the passage of currents above apredetermined value therethrough, and a plurality of washer-like membersof insulating material mounted in spaced relation on said rod to preventescape of corresponding portions of said fuse wires and arcs from saidslots.

3. A high voltage fuse having a deflnitecontinuous current rating andwhich is capable of producing an arc voltage high enough in value andwith sufficient rapidity to prevent the rise of current interruptedabove a predetermined value, comprising, in combination, an elongatedfusible element, the cross section area of said element being of a sizecapable of carrying the rated current of said fuse but which will fuseon currents above said rated current, said element having at least twospaced sections per inch of length which are reduced in area to rendersaid element faster acting at least on heavy overloads. and meanspositioned to act on the arcs formed by fusion of said fusible elementto cause the arc voltage to attain said high value at said rapid rate.

4. A high voltage fuse having a definite continuous current rating andwhich is capable of producing an arc voltage high enough in value andwith sufcient rapidity to prevent the rise of current interrupted abovea predetermined value, comprising, in combination, an elongated fusibleelement, the cross section area of said element being of a size capableof carrying the rated current of said fuse but which will fuse oncurrents above said rated current, said element having a plurality ofspaced sections reduced in area which are of a size and spacing torender said element faster acting on heavy overloads but not on lightoverloads, and to provide a plurality of spaced series arcs upon fusionof said reduced area sections, and means positioned to act on said arcsto raise the arc voltage comprising the sum of said series arcs at leastto said high value and at said rapid rate.

5. In a device of the type described having a definite continuouscurrent rating, an elongated fusible element, the cross section area ofsaid element beingr of a size capable of carrying the rated current ofsaid fuse but which will fuse on currents above said rated current, saidelement having at least two spaced sections per inch of length which arereduced in area and of a size to render said element faster acting atleast on heavy overloads but not on light overloads.

6. In a device of the type described having a definite continuouscurrent rating, an elongated fusible element, the cross section area ofsaid element being of a size capable of carrying the rated current ofsaid fuse but which will fuse on currents above said rated current, saidelement having a plurality of spaced sections reduced in area of suchsize as to render said element faster acting at least on heavy overloadsbut nothon light overloads, and to provide a plurality of spaced seriesarcs upon fusion of said reduced area sections, said reduced areasections being spaced apart a distance of from about 2 to 5 times thelarge diameter of said element. I

'7. In a current limiting fuse, a limiter unit comprising a tube ofinsulating material, terminal caps for each end of said tube, alongitudinally extending supporting rod of insulating material in saidtube and spaced from the inner walls of said tube, a plurality of spacedgenerally longitudinally extending slots in the outer surface of saidrod, a fuse wire in at least one of said slots and electricallyconnected between said terminals, spaced disks of insulating materialtelescoped over said rod to prevent escape of said fuse Wire and the arcformed upon fusion thereof entirely from said slots, and an inertgranular insulating material filling the space between said rod andtube.

8. In a current limiting fuse, a limiter unit comprising a tube ofinsulating material, terminal caps for each end of said tube, alongitudinally extending supporting rod of insulating material in saidtube and spaced from the inner walls of said tube, a plurality of spacedgenerally longitudinally extending slots in the outer surface of saidrod, a fuse wire in at least one of said slots and electricallyconnected between said terminals, at least inner wall portions of saidslots being of a material which is capable of evolving an arcextinguishing gas when in proximity with an electric arc, spaced disksof insulating material telescoped over said rod to prevent escape ofsaid fuse wire and the arc formed upon fusion thereof entirely from saidslots, and an inert granular insulating material filling the spacebetween said rod and tube.

9. In a current limiting fuse, a limiter unit comprising a tube ofinsulating material, terminal caps for each end of said tube, fusiblemeans in said tube connected between said terminals, each of said capshaving its flange extended at one side, a wire receiving groove on theouter periphery of each flange extension. and a resistance wire coilwound on the outside of said tube with end portions of said coil beingsecured in said grooves.

10. In a current limiting fuse, a limiter unit comprising a tube ofinsulating' material, terminal caps for each end of said tube, fusiblemeans in said tube connected between said terminals, each of said capshaving its flange extended at one side, a wire receiving groove on theouter periphery of each flange extension, each of said grooves havingthe inner side in the same plane as the outer edge of its cap flange,and a resistance wire coil Wound on the outside of said tube with endportions of said coil being secured in said grooves.

11. In a current limiting fuse, a limiter unit comprising a tube ofinsulating material, terminal caps for each end of said tube, fusiblemeans in said tube connected between said terminals. each of said capshaving its flange extended at one side, a wire receiving groove on theouter periphery of each flange extension, a continuous resistance wirewound on said tube in two layers with the respective layers wound inopposite directions, the ends of said wire at one end of said windingsbeing secured in one of said grooves, and an intermediate portion ofsaid wire at the 13' other end of said windings being secured in theother of said grooves.

12. A high voltage fuse which is capable of producing an arc voltagehigh enough in value and with suiiicient rapidity to prevent the rise ofcurrent interrupted above a predetermined value, comprising. incombination, an elongated fusible element. the cross section area ofsaid element being of a size capable of carrying the rated current ofsaid fuse but which will fuse on currents above said rated current, saidelement having at least one section of relatively high resistance torender said element faster acting at K least on heavy overloads but noton'light overloads, means positioned to act on the arc formed by fusionof said fusible element to cause the arc voltage to attain said highvalue at said rapid rate, and resistance means connected in a parallelcircuit with said fusible element at least after said fusible elementmelts, said resistance means being of a value such that the current willtransfer to it when said arc voltage attains a predetermined magnitudeat least sutlicient to eifect said current limitation, whereby the arcvoltage is prevented from rising beyond said predetermined magnitude,and additional fusible means connected in series with said parallelcircuit for finally interrupting the circuit, said additional fusiblemeans including a second fusible element adapted to fuse prior to saidfirst mentioned fusible element, and a low melting point alloyconnection in heat conducting relation to said second fusible elementfor interrupting the circuit on light overloads which remain on thecircuit for a predetermined time.

1 3. A high voltage fuse having a definite continuous current rating andwhich is capable of producing an arc voltage high enough in value andwith sufficient rapidity to prevent the rise of current interruptedabove a predetermined value, comprising, in combination, an elongatedfusible element, the cross section area of said element being of a sizecapable of carrying the rated current of said fuse but which will fuseon currents above said rated current, said element having a plurality ofspaced sections reduced in area to render said element faster acting atleast on heavy overloads but not on light overloads, and to provide aplurality of spaced series arcs upon fusion of said reduced areasections, said reduced area sections being so short as not tosubstantially eil'ect the time-current characteristic of said element atleast for light overloads, and means positioned to act on said arcs toraise the arc voltage comprising the sum of said series arcs at least tosaid high value and at said rapid rate.

14. A high voltage fuse having a definite continuous current rating andwhich is capable of producing an arc voltage high enough in value andwith suiiicient rapidity to prevent the rise of current interruptedabove a predetermined value, comprising, in combination, an elongatedfusible element, the cross section area of said element being of a sizecapable of carrying the rated current of said fuse but which will fuseon currents.

above said rated current, said element having a plurality of spacedsections reduced in area and of such size and spacing as to render saidelement faster acting at least on heavy overloads but not on lightoverloads, and to provide a plurality of spaced series arcs upon fusionof said reduced area sections, said element having at least 10 of saidreduced area sections, and means positioned to act on said arcs to raisethe arc voltage comprising the sum of said series arcs at least to saidhigh value and at said rapid rate.

15. A high voltage fuse having a definite continuous current rating andwhich is capable of producing an arc voltage high enough in value andwith suiiicient rapidity to prevent the rise of current interruptedabove a predetermined value, comprising, in combination, an elongatedfusible element, the cross section area of said element being of a sizecapable of carrying the rated current of said fuse but which will fuseon currents above said rated current, said element having a plurality ofspaced sections reduced in area and of such size and spacing as torender said element faster acting at least on heavy overloads but not onlight overloads, and to provide a plurality of spaced series arcs uponfusion of said reduced area sections, said reduced area sections beingspaced apart a distance of between from about 2 to 5 times the largediameter of said element, and means positioned to act on said arcs toraise the arc voltage comprising the sum of said series arcs at least tosaid high value and at said rapid rate.

16. A high voltage fuse having a definite continuous current rating andwhich is capable of producing an aro voltage high enough in value andwith -sufhcient rapidity to prevent the rise of current interruptedabove a predetermined value, comprising, in combination, an elongatedfusible element, the cross section area of said element being of a sizecapable of carrying the rated current of said fuse but which will fuseon currents above said rated current, said element having a plurality ofspaced sections reduced in area and of a size to render said elementfaster acting at least on heavy overloads but not on light overloads,and to provide a plurality of spaced series arcs upon fusion of saidreduced area sections, said reduced area sections being as short and ofas small cross section as mechanically possible and being spaced apart adistance of between from about 2 to 5 times the large diameter of saidelement, and means positioned to act on said arcs to raise the arcvoltage comprising the sum of said series arcs at least to said highvalue and at said rapid rate.

17. In a device of the type described, having a definite continuouscurrent rating, an elongated fusible element, the cross section area ofsaid element being of a size capable of carrying the rated current ofsaid fuse but which will fuse on currents above said rated current, saidelement having a plurality of sections which are reduced in area and areof such size and spacing as to render said element faster acting atleast on heavy overloads but not on light overloads.

18. In a device of the type described having a definite continuouscurrent rating, an elongated fusible element, the cross section area ofsaid element being of a size capable of carrying the rated current ofsaid fuse but which will fuse on currents above said rated current, saidelement having a plurality of spaced sections which are reduced in areaand substantially as short as mechanically possible to render saidelement faster acting at least on heavy overloads.

19. In a device of the type described having a definite continuouscurrent rating, an elongated fusible element, the cross section area ofsaid element being of a size capable of carrying the rated current ofsaid fuse but which will fuse on currents above said rated current, saidelement having a pluarlity of sections which are reduced in area and ofsuch size and spacing as not to substantially alter the time-currentcharcteristic of said element on overloads up to a predetermined valueabove which the melting time of said element is substantially'decreased.

20. In-a device of the type described having a definite continuouscurrent rating, an elongated fusible element, the cross section area ofsaid element being of a size capable of carrying the rated current ofsaid fuse but which will fuse on currents above said rated current, saidelement having a plurality of sections which are reduced in area and ofsuch small size and sufficient spacing as not to substantially altervthe time-current characteristic of said element on overloads up to apredetermined value above which the melting time of said element issubstantially decreased.

21. Current limiting cirucit interrupting means comprising, means of asolid insulating material forming an elongated arc passage, means forstriking an arc in said passage, said passage being suiiiciently narrowto restrict the cross section of the arc, said arc passage closelysurrounding the arc throughout its length on at least three sides, withthe fourth side of said passage being open at longitudinally spacedpoints, to permit correspondingly spaced portions of said arc to loopoutwardly through said openings and the escape of arc products whilemaintaining in termediate portions of the arc in the restrictivepassage. and a layer of inert granular means of insulating material oversaid openings for cooling and dispersing products of the arc.

22. Current limiting circuit interrupting means comprising, means of asolid insulating material forming an elongated arc passage, means forstriking an arc in said passage, said passage being suiliciently narrowto restrict the cross section of the arc, said arc passage closelysurrounding the arc throughout its length on at least three sides, withthe fourth side of said passage being open at longitudinally spacedpoints, to permit correspondingly spaced portions of said arc to loopoutwardly through said openings, at least inner wall portions of saidpassage being of an insulating material which is capable of evolving anarc extinguishing gas when in proximity to an electric are. so that whensaid arc is struck said arc extinguishing gas will ilow laterally acrossthe arc to escape through said openings and thereby cause looping of atleast spaced portions of the arc toward said openings and the escape ofare products while maintaining intermediate portions of the arc in therestrictive passage, and a layer of inert granular means of insulatingmaterial over said openings for cooling and dispersing products of thearc.

23. In a circuit interrupter, arc establishing means, a mass of inert.insulating material of granular form having a high thermal capacity,means supporting said insulating material in proximity to at least oneside of the path of an arc struck by said arc establishing means, saidinsulating material being directly exposed to substantially the entirelength of said path, means of a solid insulating material capable ofevolving an arc-extinguishing gas when in proximity to an electric arcsupported in proximity with at least the opposite side of said arc pathalong substantially the entire length thereof to cause a blast ofunionized gas to iiow through substantially the entire length of the arcin a direction toward said granular insulating material to disperse'themetal vapor in the arc through said granular insulating material whereit is condensed in nely divided form outside the' arc path, and spacedmeans of solid insulating material for maintaining correspondinglyspaced p01'-v tions of said arc in proximity with said gas evolvingmaterial, whereby portions of the arc intermediate saidspaced means maybe looped outwardly. toward said granular material by the passagetherethrough of said evolved gases, but the arc is prevented from movingbodily away from said gas evolving material by said spaced means ofinsulating material.

24. In a current limiting fuse, a fusibler wire,

supporting means of a solid insulating material i surrounding said wireat a plurality of spaced points, said material having at least innerwall portions capable of evolving an arc extinguishing gas when inproximity to an electric arc and having one internal dimension which issmall enough to restrict the cross section of the arc formed upon fusionof said wire to thereby limit the arc current, and a nely divided inertinsulating material in proximity to said fusible wire intermediate saidspaced points.

25. In a circuit interrupting means, means of a solid insulatingmaterial forming an elongated arc passage, means for striking an arc insaid passage, said passage being suiiiciently narrow to restrict thecross section of the are, said respondingly spaced portions of said arcto loop outwardly through said openings and the escape of arc productswhile maintaining intermediate portions of the arc in the restrictivepassage, a layer of inert granular means of insulating material oversaid openings for cooling and dispersing products of the arc, and saidmeans of solid insulating material including barriers extendinglaterally outwardly at points intermediate said vent openings.

HERBERT L. RAWLINS.

HAROLD H. FAHNOE'.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,327,777 Randall Jan. 13, 19201,540,119 Glowack June 2, 1925 1,545,550 Coates July 14, 1925 1,696,605Hollnagel Dec. 25, 1928 1,849,875 Kees Mar. 15, 1932 1,927,905 SlepianSep. 26, 1933 1,966,901 McMahon July 17, 1934 2,013,427 Starr Sep. 3,1935 2,142,356 Hastings Jan. 3, 1939 2,157,906 Lohausen May 9, 19392,209,823 Lohausen July 30, 1940 2,230 207 Thommen et al Jan. 28, 19412,309,013 Rawlins et al. July 19, 1943 2,337,495 Rawlins Dec. 21, 19432,337,504 Strom Dec. 21, 1943 2,354,134 Ludwig et al July 18, 19442,414,344 Suits Jan. 14, 1947 FOREIGN PATENTS Number Country Date 20,409Great Britain May 23, 1912 450,970 Great Britain July 27, 1936

